Synthetic turf sometimes has an undesirable tendency to build up static charge in itself as well as the persons who walk or play on it. This may cause static electrical shocks to the body. Surprisingly, static charge build up is known to occur even in high humidity environments such as found in regions like Florida during the summer months.
Static charge is particularly problematic on playgrounds where playground equipment is often constructed of insulating materials that also have a propensity to build up static charge. Synthetic turf can act as insulator so that even when a static charge is created on a piece of playground equipment such as a slide it is not dissipated as a person walks across the turf until a conductive ground, such as a metal pole, is touched.
Conventional ways to solve the static problem in synthetic turf have not worked. For instance Brunswick Corporation U.S. Pat. No. 4,356,220 describes an artificial grass product comprising: a pile fabric with yarn comprised of a plurality of fibers made of a polymeric material. This patent teaches that additives, such as antistatic agents, can be dispersed in the fibers.
Meanwhile, U.S. Pat. No. 4,672,005 issued in the name of Dyer describes a process for improving the hygroscopic and soil release properties of a polymer substrate in which the substrate is contacted with a suitable aqueous mixture containing a water soluble vinyl monomer and a hydrophobic vinyl monomer. This patent alleges that antistatic properties with this process are improved.
Antistatic polymer additives have been used to solve this problem but have been found to be ineffective because they may cause a deterioration of fiber extrusion performance and fiber physical properties. In addition, static dissipation of the turf is inadequate to render a noticeable benefit.
Antistatic topical additives such as glyceryl monostearate or octadecylbis (2-hydroxyethyl) amine, sold under the tradenames Armostat™ 1000 beads, and Armostat™ by Akzo Nobel Polymer Chemicals B.V. of the Netherlands which may be applied to fiber during manufacture have also been used. But these have also been found to be ineffective as they are not substantive solutions for outdoor environments, especially in the presence of rain.
Other ways of solving this problem have been the topical application of antistatic chemicals, such as Staticide™ sold by Amstat Industries of Glenview, Ill., directly to the synthetic turf. While effective in some situations, this solution is limited since topically applied chemicals are not substantive solutions for outdoor environments, especially in the presence of rain.
Meanwhile, the problem of static shock has been addressed in carpet by incorporating an electrically conductive fiber into pile yarn used to make the carpet. U.S. Pat. No. 3,971,202 issued in the name of Windley for instance describes cobulking electrically conductive sheath-core filaments such as those disclosed in U.S. Pat. No. 3,803,453 issued in the name of Hull with nonconductive filaments to form a crimped, bulky carpet yarn. This carpet yarn may dissipate static electricity charges which are annoying to people who walk on nonconductive carpets when humidity is low. In this instance the, conductive filaments are tangled with the carpet tufts so that they extend the full length of the carpet tuft.
U.S. Pat. No. 4,612,150 issued in the name of De Howitt describes introducing spin-oriented electrically conductive bicomponent filaments into a quench chimney wherein nonconductive filaments are melt spun and cooled, combining the conductive and nonconductive filaments at a puller roll, drawing and cobulking the combined yarn and then winding up the yarn.
These conventional approaches are problematic with synthetic turf since it is not practically possible to cobulk electrically conductive filaments with nonconductive filaments. This is because turf fibers are typically monofilament or slit tape. Because synthetic turf fibers are large, it is not possible to combine the antistatic yarn with synthetic turf fiber in such a way that the two yarns are intimately entangled as is characteristically done in carpet.
Another problem in the art which is unique to synthetic turf is the use of infill. Synthetic turf incorporates the use of infill. This is a particulate material that is incorporated onto the turf face between tufts. The purpose of infill is to hold tufts upright and to provide a cushion on which to play. These materials are typically all insulators and thus exacerbate static electricity as understood by one of ordinary skill in the art.